Sheet metal threaded article

ABSTRACT

A thin sheet of metal is drawn in progressive steps to form a hollow body having a closed end tubular portion integrally connected to an outwardly projecting cup-shaped flange portion. A section of the tubular portion is crimped inwardly against a threaded mandrel to form helical threads and diametrically opposed and outwardly projecting double wall rib portions. The mandrel is unthreaded to form a sheet metal insert which is adapted to be supported within a mold cavity by a cylindrical support pin during injection of a plastics material into the cavity and around the insert. The threads and rib portions positively secure the sheet metal insert within the molded plastics article or part for receiving a threaded fastener. The insert may also be used in a metal part or casting or in a wood article, wherever threads are required or desirable.

BACKGROUND OF THE INVENTION

In the art of injecting a plastics material into a mold cavity to form amolded plastics article or part such as, for example, a control knob ora pump housing or an enclosure cabinet, it is common to provide the partwith one or more threaded holes for receiving a threaded fastener whichconnects the part to another article or part. When it is necessary toprovide the threaded hole with internal threads having substantialstrength and capable of withstanding substantial axial and torsionalforces, a metal insert is commonly positioned within the mold cavity ona support stud or pin prior to injecting the plastics material. When themolded plastics part is removed from the mold cavity, the metal insertremains with the molded part and provides a threaded hole for receivinga threaded connector or fastener.

Usually, the metal insert is formed or machined from solid bar stock onan automatic screw machine, for example, as disclosed in U.S. Pat. No.1,919,455. The machine automatically drills and taps a hole within oneend of the bar stock and also roughens or knurles the outer surface ofthe bar stock after which the bar stock is automatically cut off to forma metal insert of predetermined length. The roughened or knurled outersurface of the insert receives the injected plastics material and formsa positive connection of the insert with the molded part of plasticsmaterial. When the molded part is used in a high moisture or corrosiveenvironment, it is desirable for the metal insert to be machined from anon-corrosive material such as aluminum, brass or stainless steel. Sucha material and the machining operation significantly increase the costof the metal insert and thereby result in increasing the cost of themolded plastic article or part.

SUMMARY OF THE INVENTION

The present invention is directed to an improved sheet metal threadedarticle or insert which is ideally suited for forming a high strengththread-forming hole within a part such as a part molded of a plasticsmaterial, and to the method of producing the article or insert. As usedherein, the term part is intended to include any type of article, objector body of metal, wood or plastics material. As a primary advantage, thesheet metal article or insert of the invention provides forsignificantly decreasing the cost of forming high strength metal threadswithin a hole form in a molded plastics part by significantly reducingthe cost of manufacturing a metal insert which has internal threads andrigidly bonds to the molded plastics material.

In general, the above features and advantages are provided in accordancewith one embodiment of the invention by progressively drawing a thinsheet or disc of metal such as 0.010 inch aluminum or brass, to form anelongated body having a closed end tubular portion integrally connectedto an outwardly projecting base or flange portion. Preferably, theflange portion has a cup-like configuration, and the tubular portion iscrimped inwardly against a threaded mandrel to provide the tubularportion with a restricted threaded section and a pair of outwardlyprojecting and diametrically opposed ribs each having a thickness doublethe sheet metal thickness. The tubular section is then unthreaded fromthe mandrel.

The sheet metal thread-forming insert is supported within a mold cavityby a cylindrical pin having an outside diameter substantially the sameas the inside diameter of the crimped thread section of the metalinsert. When the plastics material is injected into the mold cavity, thematerial surrounds the crimped thread section and the outwardlyprojecting ribs to form a substantially high resistance to the pullingand torsional forces acting on the insert when a threaded fastener istightened within the insert. The closed end of the tubular portion isnecessary to prevent the plastics material from filling the entiretubular portion.

Other features and advantages of the invention will be apparent from thefollowing description, the accompanying drawing and the appended claims.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an enlarged perspective view of a sheet metal thread forminginsert constructed in accordance with the invention;

FIG. 2 is a diagrammatic illustration of the progressive drawing andforming steps used to produce the insert shown in FIG. 1;

FIG. 3 is an axial section of the sheet metal insert shown in FIG. 1 andillustrating its support within a mold cavity;

FIG. 4 illustrates the sheet metal insert as embedded within theplastics part molded within the cavity shown in FIG. 3; and

FIG. 5 is a fragmentary radial section taken generally on the line 5--5of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with the invention, an insert is formed of sheet metalhaving a thickness within a range of 0.002 to 0.050 inch such as theinsert 10 which is formed of 0.010 inch brass. The insert 10 consists ofa hollow body formed by a tubular portion 12 having a closed end wall 13(FIG. 3) and an open end defined by an outwardly projecting andintegrally connected annular base or flange portion 14. The flangeportion 14 includes an outer cylindrical skirt portion 16 and a taperedor frusto-conical inner portion 17 which cooperate to form a cup-shapedconfiguration. The tubular portion 12 includes an inwardly crimpedportion or section 22 which define helical threads 23 and also includesa pair of outwardly projecting and axially extending ribs 26 which arediametrically opposed. As shown in FIG. 5, each of the ribs 26 has athickness which is double the sheet metal thickness, and the double wallthickness provides the rib with substantial rigidity.

Referring to FIG. 2, the sheet metal insert 10 is manufactured orproduced by drawing a circular blank or disc 30 of the brass sheet metalin a series of progressive steps until the flange portion 14 projectsfrom a cylindrical portion 32 having an outside diameter the same as thecylindrical end portion 12 described above. A mandrel 34 having externalthreads 36, is then inserted into the tubular or cylindrical portion 32,after which the cylindrical portion 32 is crimped inwardly against themandrel 34 by a pair of mating or split external dies (not shown) toform the crimped section 22 and the threads 23 and ribs 26 within thetubular body portion 32. After the crimping operation which is the laststep in forming the insert 10, the mandrel 34 is unthreaded from theinsert 10 or the insert 10 is unthreaded from the mandrel 34, whicheveris desired.

Referring to FIG. 3, an insert 10 is supported within a cavity 42 of aninjection mold 45 by a cylindrical support pin 46 which is secured tothe mold 45 and projects into the cavity 42. Preferably, the mold 45includes an annular portion 48 which defines a counterbore or recess 49for receiving the cup-shaped flange portion 14 of the insert 10. Theoutside diameter of the support pin 46 is substantially the same as theinside diameter of the threads 23 and slightly smaller than the insidediameter of the cylindrical end portion 12. The cylindrical end portion12 has an inside diameter which provides sufficient clearance forreceiving the threads of a fastener (not shown) threaded into theinsert.

When the molded plastics material is injected into the mold cavity 42,the material flows into the crimped section 22 and between the threads23 and around the ribs 26. After the plastics material hardens to form amolded plastic article or part P (FIG. 4), the part is removed from themold cavity with the sheet metal insert 10 embedded within the part, asillustrated in FIG. 4. In accordance with one experiment, the part Pconsisted of a pump housing for an automatic dishwashing machine and wasmolded from a thermosetting plastics material with four uniformly spacedsheet metal inserts 10. The inserts were spaced to receive correspondingmachine screws which secure the pump housing to an electric motor.

From the drawing and the above description, it is apparent that a sheetmetal insert constructed in accordance with the invention, providesdesirable features and advantages. For example, as one importantfeature, the sheet metal insert 10 significantly reduces the cost forforming non-corrosive metal threads within an article such as a part ofa molded plastics material. In fact, the insert may be made ofnon-rusting brass at a lower cost than a screw machine insert made ofsteel, and such non-rusting is very important, particularly whendisassembly is required after an extended period of time.

As another important feature, the reduced or crimped thread section 22and the outwardly projecting double wall ribs 26 provide for positivelysecuring the sheet metal insert within the article so that the insertwill withstand substantial torsional forces as well as axial tensionforces when a screw or fastener is threaded into and tightened withinthe insert. The thin gauge of the sheet metal insert 10 also minimizesthe weight of the insert which not only contributes to the lowmanufacturing cost of the insert but also contributes to minimizing theweight of the molded plastic part P which receives one or more of theinserts. The sheet metal insert 10 may also be efficiently andeconomically produced from sheet metals other than brass sheet metal,such as cold rolled steel, stainless steel or copper, depending upon therequirements of the insert and/or the environment in which the insert isused. As mentioned above, the insert may also be used in an articleformed of a material other than a plastics material, such as a metalcasting or a wood base material, and may be secured within a hole in thearticle by adhesive or riveting or a press-fit.

While the sheet metal insert and its method of production hereindescribed constitute a preferred embodiment of the invention, it is tobe understood that the invention is not limited to the precise sheetmetal insert and method described, and that changes may be made thereinwithout departing from the scope and spirit of the invention as definedin the appended claims.

The invention having thus been described, the following is claimed:
 1. Asheet metal threaded article comprising a drawn sheet metal hollow bodyhaving an elongated tubular portion projecting from an integrallyconnected base portion defining an opening, said tubular portionincluding an inwardly crimped tubular section having a corrugated wallconfiguration in axial cross-section and forming helical threads, saidinwardly crimped tubular section including at least one axiallyextending folded sheet metal rib of double wall thickness, and saidhelical threads being adapted to receive a threaded member.
 2. A sheetmetal article as defined in claim 1 in combination with a solid materialsurrounding said tubular portion of said sheet metal body, and said ribprojects outwardly into said material to prevent rotation of said bodywithin said material when the threaded member is tightened.
 3. A sheetmetal threaded article adapted to be inserted into a hardenable materialto form a threaded hole within a part molded of the material, saidarticle comprising a drawn sheet metal hollow body having an elongatedtubular portion projecting from an integrally connected base portiondefining an opening, said tubular portion including an inwardly crimpedtubular section having a corrugated wall configuration in axialcross-section and forming helical threads, said inwardly crimped tubularsection including a plurality of circumferentially spaced and axiallyextending folded sheet metal ribs each having a double wall thickness,said inwardly crimped tubular section being effective to retain saidbody within the material in response to receiving a threaded member, andsaid ribs being effective to prevent rotation of said body within thematerial when the threaded member is tightened.
 4. A sheet metal articleas defined in claim 2 wherein said base portion of said sheet metal bodyis cup-shaped for receiving the solid material.
 5. A sheet metal articleas defined in claim 1 wherein said crimped section has two diametricallyopposite said ribs.
 6. A sheet metal article as defined in claim 1wherein said drawn sheet metal body has a wall thickness within therange of 0.002 inch to 0.050 inch.
 7. A sheet metal article as definedin claim 1 wherein said rib projects radially outwardly by a distancesubstantially greater than the thickness of said sheet metal formingsaid body.
 8. A sheet metal article as defined in claim 3 in combinationwith a body of molded plastics material surrounding said tubular portionof said body.
 9. A sheet metal article as defined in claim 1 whereinsaid tubular portion includes a generally cylindrical cup-shaped endportion closing the inner end of said body.
 10. A sheet metal article asdefined in claim 9 wherein said end portion has an inner diameterslightly greater than the inner diameter of said threads.
 11. A sheetmetal article as defined in claim 3 wherein said tubular portionincludes a generally cylindrical cup-shaped inner end portion.